Regulations relating to fire safety have become more stringent in recent years. For example, one aspect of relatively new Federal Regulations relating to handicapped persons is the requirement for visual fire warning systems for the hearing-impaired in various types of public spaces. Visual alarms using strobe lights are well-known and in widespread use, primarily in industrial and vehicular settings. They will in the future be more frequently installed in public spaces in institutional and commercial buildings, not only when required but as a preferred safety practice.
Strobe lamps are elongated tubes. As such, the light they produce is not uniform in all directions. The light that radiates perpendicularly from the lamp relative to its axis is of uniform intensity. However, the light output in the plane of the lamp axis diminishes substantially as a function of the cosine of the angle between the radial line in the plane and all other lines. Near and at + and -90.degree., i.e., when the lamp is observed from either end, the light output is but a small fraction of its output in the radial direction.
Underwriters Laboratories (UL.RTM.) has recently adopted standards that require certain levels of light output from strobe alarm lights for fire safety warning systems in (1) a plane perpendicular to the lamp axis and (2) the plane that is perpendicular to that plane and includes the lamp axis. (Throughout this specification, the term "light" refers to a system that consists of a strobe lamp bulb, a support that may include a reflector, and a lens, and the term "lamp" refers to the light-emitting strobe light bulb element.)
One way of meeting the requirement is to equip the strobe light with two lamps, one perpendicular to the other. That way is costly and also requires more electric current, which for a given battery storage capacity reduces the operating time of the device or for a given operating time requires more battery storage capacity, another additional cost. Another possible way of meeting the UL.RTM. requirement for plane 2 is with a specially designed lens, but that means diverting light and thus requires reducing the light output in directions other than plane 2.
U.S. patent application Ser. No. 08/031,949 (Jongewaard, filed Mar. 16, 1993), which is owned by the assignee of the present invention, describes and shows a reflector for a strobe warning light that provides enhanced light output at high angles from the radial in the plane of the lamp axis and a high light output for a given lamp output at all angles in planes perpendicular to the lamp axis, thereby permitting the lamp current draw to be kept low for any given light output. The enhanced light output at high angles with respect to the radial line in the plane of the lamp axis is obtained by concave reflective surfaces on "wings" of the reflector adjacent each end of the lamp. High efficiency of light utilization in the plane perpendicular to the lamp axis is obtained by a semicylindrical concave reflective surface of the reflector having as its axis the axis of the lamp. The axis of the lamp is located at or above the edges of the semicylindrical reflective surface and the wings. The respective wings are located on opposite sides of a reference plane perpendicular to the base plane of the reflector that includes the lamp axis, and the reflective surfaces of each wing is configured and oriented such that it reflects light generally parallel to the lamp axis along the same side of the reference plane on which it is located. Inasmuch as the present invention, preferably, includes wings of the type described and shown in the above-mentioned Jongewaard application, it is hereby incorporated into the present specification by reference.
Underwriters Laboratories has established requirements for the light output of strobe warning lights that are mounted on a wall that are different from those established for strobe warning lights that are mounted on a ceiling. The requirements for wall strobe warning lights permits lesser light output at high angles approaching the vertical and do not require any light output above a horizontal plane, i.e., toward the ceiling. These requirements present opportunities for modifying the light output of a plain (bare) strobe lamp by a reflector that makes maximum use of the available light from the lamp.